In an effort to reduce back pain through early intervention techniques, some investigators have focused upon nerves contained within the vertebral bodies which are adjacent the problematic disc.
For example, PCT Patent Publication No. WO 01/0157655 (“Heggeness”) discloses ablating nerves contained within the vertebral body by first boring into the vertebral body with a nerve ablation device, placing the tip of the device in close proximity to the nerve, and then ablating the nerves with the tip. Heggeness discloses using laser devices, electricity transmitting devices, fluid transmitting devices and thermal devices, and devices for carrying either chemotherapeutic or radioactive substances as candidate nerve ablation devices.
In describing techniques using electricity transmitting devices, Heggeness discloses “raising the temperature of tip 24 such that the intraosseous nerve is ablated by the heat generated by electrical current passing through tip.” See Heggeness at 8, 28.
Heggeness further discloses multiple methods of accessing the intraosseous nerve (ION). However, each of these methods essentially disclose either i) boring a straight channel into the vertebra such that placement of an electrode tip near the end of that channel will bring the electrode tip sufficiently close to the ION to effect its ablation, or ii) accessing the basivertebral nerve (BVN) via the vertebral foramen. None of these techniques recognize how to effectively carry out nerve ablation when the precise locations of the ION is unknown, or when the electrode tip can not be maneuvered relatively close to the ION.
EPO Patent Published Patent Application No. EP 1 059067 A1 (“Cosman”) discloses ablative treatment of metastatic bone tumors, including those within the spine. Pain relief is reportedly achieved by penetrating the bone wall with a suitable probe, and applying heat through the probe to ablate either the bone tumor or the tissue near the bone tumor. Cosman teaches the use of both monopolar and bipolar probes in this application. Cosman also teaches that the treatment may also be used to ablate the nerves and nerve ramifications in and/or around the bone to desensitize them against farther tumor encroachment. See Cosman at col. 11, lines 7-11.
However, monopolar approaches require the use of a grounding pad beneath the patient and allows energy to flow from the probe and to dissipate in the surrounding tissue. Because the path by which the energy flows from a monopolar probe to its corresponding pad is uncontrolled, the energy may undesirably flow through sensitive tissue, such as the spinal cord. Since this method may cause undesired local muscle or nerve stimulation, it may be difficult or dangerous to operate in sensitive areas of the human body.
Cosman discloses devices whose electrodes can deviate from the axis of the access channel. In particular, Cosman discloses steerable tips, spring-like electrodes that take a straight shape within the catheter and then curve upon exiting the catheter. Cosman discloses that the curved portion of the electrode may be a rigid and rugged permanent curve, or it may be a flexible configuration so that it can be steered, pushed or guided by the clinician to be positioned at various location. See Cosman at col. 8, lines 40-50). Cosman discloses that electrodes may comprise tubing made of elastic or super-elastic metal such as a spring steel or nitonol tubing so that the electrode can be inserted into straight segments of the cannula and still describes a curved path when the curved portion emerges from the opening. See Cosman at col. 10, lines 11-16. Cosman also discloses an electrode having a flexible but steerable tip which can define an arc, as set by the physician. See Cosman at col. 14, line 3.
In sum, Heggeness and Cosman disclose methods of treating that assume the tip of the electrode can be directed substantially to the target tissue.
A few investigators have examined the effectiveness of heating bone with monopolar RF electrodes. DuPuy, AJR: 175, November 2000, 1263-1266 noted decreased heat transmission at a 10 mm distance from the electrode through cancellous bone in ex vivo studies. DuPuy notes that local heat sinks from the rich epidural venous plexus and cerebrospinal fluid pulsations may account for the decreased heat transmission in cancellous bone. Tillotson, Investigative Radiology, 24:11, November 1989, 888-892, studied the percutaneous ablation of the trigeminal ganglion using RF energy, and found that bone marrow necrosis was limited to a sphere of about 1 cm in diameter, regardless of the probe size and duration of heating. Tillotson further reports that Lindskog showed that the transmission of heat within bone is sharply limited by blood flow, and that lethal temperatures cannot be sustained over great distances.
In sum, these investigators appear to report that the well-vascularized nature of bone appears to limit the heating effect of RF electrodes to a distance of less than about 0.5 cm from the tip.
U.S. Pat. No. 6,312,426 (“Goldberg”) discloses a system of RF plate-like electrodes for effecting large, uniform, and extended ablation of the tissue proximate the plate-like electrodes. In some embodiments, the plate-like electrodes are placed on the surface of the body tissue, where the ablation is desired, and are configured to lie approximately parallel or opposing one another, such that they make a lesion by coagulating most of the body tissue volume between them. Goldberg appears to be primarily directed to the treatment of tumors. Goldberg states that one advantage of the system is that the surgeon need not determine the precise position of the tumor. See Goldberg at col. 3, line 59-60. Goldberg does not appear to specifically discuss the treatment of nerves.
U.S. Pat. No. 6,139,545 (“Utley”) discloses a facial nerve ablation system including at least two spaced apart bi-polar probe electrodes spanning between them a percutaneous tissue region containing a facial nerve branch. Utley teaches that the size and spacing of the electrodes are purposely set to penetrate the skin to a depth sufficient to span a targeted nerve or nerve within a defined region. See col. 5, lines 44-47. Utley further teaches that the system makes possible the non-invasive selection of discrete motor nerve branches, which are small and interspersed in muscle, making them difficult to see and detect, for the purpose of specifically targeting them for ablation. See col. 2, lines 20-24. Utley does not disclose the use of such a system for the treatment of IONS, nor rigid probes, or deployable electrodes. The probes of Utley